JS Object: Force Property Value to be a certain Type

Question

Is there a way to make sure the input for a property is a certain Type? In this example I want to check whether the new Lion has a mane. Is there a way to make sure that the 'mane' value is a Boolean, when creating a new Lion Object?

function Lion(height, weight, fur, purr, mane) {
  Cat.call(this, name, height, weight, fur, purr);
  this.name = 'Lion';
  this.mane = mane;
};

var lion1 = new Lion('100cm', '250kg', 'beige', 'ROAAAAAAAAR!', true);

You could add TypeScript to your project and get transpile time errors if your types dont match. Or when you use it prepend to ensure the cast. — rjustin, Sep 14 '17 at 20:59
You can create a set method that modifies that variable, and in that method check the type of the data — Frankusky, Sep 14 '17 at 21:00
Do you want to reject a non-boolean, or convert it to the equivalent boolean? — Barmar, Sep 14 '17 at 21:16

score 0 · Answer 1 · edited Sep 14 '17 at 21:15

0

You could force whatever mane is to be a boolean by using Boolean(mane) it will output true/false based on Javascript truthy/falsey values and always guarantree mane is a boolean.

this.mane = Boolean(mane);

edited Sep 14 '17 at 21:15

Barmar

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answered Sep 14 '17 at 21:00

AHB

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I think `!!mane` is the more idiomatic way to do this. It doesn't call a function or box it into an object. – Barmar Sep 14 '17 at 21:16
Sure the output is the same but for someone not familiar with JS putting !! in front of a variable name is probably not very readable. – AHB Sep 14 '17 at 21:20
You could link to this question: https://stackoverflow.com/questions/784929/what-is-the-not-not-operator-in-javascript/784946#784946 – Barmar Sep 14 '17 at 21:23

score 0 · Answer 2 · answered Sep 14 '17 at 21:00

0

You can use the typeof operator to perform that check when creating the new object:

function Lion(height, weight, fur, purr, mane) {
  Cat.call(this, name, height, weight, fur, purr);
  this.name = 'Lion';
  if (typeof mane === "boolean") {
    this.mane = mane;
  } else {
    throw "type error" // or do whatever
  }
};

answered Sep 14 '17 at 21:00

nvioli

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That seems to work best for me right now(still beginner level). Thank you @nvioli! – Vincent Sep 14 '17 at 22:48

JS Object: Force Property Value to be a certain Type

2 Answers2